Aluminum die casting alloy

ABSTRACT

The thermal conductivity of the alloy of the invention can achieve 146 W/m·K, an increase of 45% compared with that of common aluminum die casting alloy-ADC12. The casting defects like shrinkage cavity, micro-porosity and amount of dross also become much less than those of pure aluminum. Further, the fluidity and mold erosion resistance of this alloy is also better than that of pure aluminum and almost equivalent to that of ADC12. When the aluminum die casting alloy of the invention is applied to a heat sink, the thermal resistance is even lower than that of ADC12 and 1070 pure aluminum.

[0001] This is a continuation-in-part of Ser. No. 09/527,879, filed Mar.20, 2000, now pending.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an aluminum die casting alloy,and more particularly to an aluminum die casting alloy used for a heatsink. The aluminum die casting alloy possesses good castability, highthermal conductivity and minor mold erosion.

[0004] 2. Description of the Prior Art

[0005] As the power dissipation of IC components and assemblies such asCPU, chipsets and the like increases, so does the demand for thermallyconductive materials. The heat generated by the increasing powerdissipation of the IC component, if not effectively dispensed with, willeasily cause the IC component or even the entire system to experienceinstability or failure. In order to dissipate the heat from the ICcomponent and keep the junction temperature below the operating limit, aheat sink or heat dissipation apparatus is always mounted on the topsurface of IC components.

[0006] Heat sink units are mainly fabricated by either extrusion or diecasting. Among these, aluminum die casting is widely employed to producevery compact heat sink units despite their complex shape and flexibledesign. However, the common aluminum die casting alloys such as ADC12and ADC10 possess an inferior thermal conductivity (K=96 W/m·K) ascompared one of pure aluminum (220 W/m·K). Therefore, the commonaluminum die casting alloy is gradually becoming unable to meet therequirements of high speed and high power CPUs. Although the rawmaterial of pure aluminum has a superior thermal conductivity, when usedas a die casting material, its poor melt fluidity and serious castingdefects such as shrinkage cavity, micro-porosity and dross willeliminate the substantial thermal conductivity of the original rawmaterial. Consequently, the total thermal performance of the purealuminum heat sink is counterbalanced by the casting defects. Further,the die casting mold is easily eroded by the molten pure aluminum ascasting proceeds, thus reducing the lifetime of the metal mold.

SUMMARY OF THE INVENTION

[0007] The object of the present invention is to solve theabove-mentioned problems and to provide a suitable aluminum die castingalloy which possesses superior thermal conductivity, better castingsoundness and mechanical properties; as well as a good erosionresistance to the metal mold process.

[0008] To achieve this object, a new aluminum die casting alloy isdeveloped by metallurgical design. The thermal conductivity of thealuminum die casting alloy of the present invention can achieve 146W/m.K, an increase of 45% compared with the commercial aluminumalloy—ADC12 . When this aluminum die casting alloy is used as a heatsink material, the casting defects like shrinkage cavity, micro-porosityand amount of dross become much less than those of pure aluminum.Consequently, the thermal resistance of this alloy is even lower thanthat of pure aluminum. That is to say, the thermal performance of theheat sink of this alloy is better than that of pure aluminum and ADC12.Further, the melt fluidity and mold erosion resistance of this alloy isalso better than that of pure aluminum and almost equivalent to that ofADC12. Therefore, the aluminum die casting alloy of the presentinvention has the potential to substitute for the pure aluminum and thecommon die casting alloys for a heat sink material of CPUS, DRAMs, BGAs,and chipsets. The alloy of the present invention can even be used as achassis material for computer, hard disk, CD-ROM, power supply and otherIC-related applicationss.

BRIEF DESCRIPION OF THE DRAWINGS

[0009] The present invention will be described in detail with referenceto the illustrated embodiments and the accompanying drawings, in which:

[0010]FIG. 1 shows a photograph of the cross section of a die cast heatsink using 1070 pure aluminum;

[0011]FIG. 2 shows a photograph of the cross section of a die cast heatsink using the aluminum alloy of this invention;

[0012]FIG. 3 shows a photograph of the die cast microstructure of theA514 aluminum alloy (with micro-shrinkage and porosity);

[0013]FIG. 4 shows a photograph of the die cast microstructure of theinvented aluminum alloy (with no micro-shrinkage);

[0014]FIG. 5 shows a photograph of a misrun that occurred when usingA514 alloy as heat sink material; and

[0015]FIG. 6 shows a photograph of sound casting by using the inventedalloy as heat sink material; and

[0016]FIG. 7 shows the X-ray diffraction pattern of A383, A384 and theinvented alloy.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The aluminum die casting alloy of this invention possesses goodcasting soundness as a commercial aluminum die casting alloy, highthermal conductivity between that of ADC12 and pure aluminum, and minormold erosion.

[0018] Table 1 is the chemical composition of the aluminum die castingalloy of the present invention and the commercial aluminum die castingalloys. TABLE 1 Aluminum alloy Composition (wt %) ASTM (JIS) Si Cu Mg ZnFe Mn Ni Sn Al A413 11.0˜1.30 <1.0 <0.3 <0.5 <1.3 <0.3 <0.5 <0.1 Bal.(ADC1) A360  9.0˜10.0 <0.6 0.4˜0.6 <0.5 <1.3 <0.3 <0.5 <0.1 Bal. (ADC3)A518 <0.3 <0.2 4.0˜8.5 <0.1 <1.8 <0.3 <0.5 <0.1 Bal. (ADC5) A514 <1.0<0.1 2.5˜4.0 <0.4 <0.8 <0.3 <0.5 <0.1 Bal. (ADC6) A380 7.5˜9.5 2.0˜4.0<0.3 <1.0 <1.3 <0.3 <0.5 <0.3 Bal. (ADC10) A383  9.6˜12.0 <1.0 <0.3 <1.0<1.3 <0.3 <0.5 <0.3 Bal. (ADC12) A390 16˜18 4˜5 0.45˜0.65 <0.1 <1.3 <0.1<0.1 <0.1 Bal. (ADC14) The alloy of 10.5   6.0  0.24  0.6  0.68  0.15  0.005  0.01 Bal. the invention

[0019] Table 2 is the thermal conductivity of the aluminum die castingalloy of the present invention and commercial aluminum die castingalloys. TABLE 2 Aluminum alloy Thermal ASTM (JIS) conductivity (W/M · K)A413 (ADC1) 121 A360 (ADC3) 113 A518 (ADC5)  96 A514 (ADC6) 138 A380(ADC10)  96 A383 (ADC12)  96 A390 (ADC14) 134 The alloy of the invention146

[0020] From the results, it can be seen that thermal conductivity of thealloy of the invention can achieve 146 W/m·K, an increase of 45%compared with that of ADC12.

[0021] When the aluminum die casting alloy of the invention is appliedto a CPU heat sink for a desktop PC, it can be seen that thermalresistance decreases from 1.03° C./W to 0.89° C./W, which is less thanthat of ADC12, as shown in Table 3. TABLE 3 Input Ambient Case PowerTemperature Temperature Rca* Material (W) (° C.) (° C.) (° C./W) MarkADC12 19.46 24.2 44.3 1.03 Forced 27.4  24.3 55.2 1.02 convection 34.8924.4 60.4 1.03 with cooling fan The 19.98 24.3 42   0.89 Forced alloy of28.07 24.7 49.6 0.89 convection the in- 35.8  24.9 56.5 0.89 withvention cooling fan

[0022] When the aluminum die casting alloy of the invention is appliedto a CPU heat sink of a notebook PC, it can be seen that the casetemperature is lower than that using 1070 pure aluminum by about 4° C.,as shown in Table 4. Moreover, the castability of the aluminum diecasting alloy of the invention is better than 1070 pure aluminum. FIG. 1is the cross section of a die cast heat sink using 1070 pure aluminum.It shows a greater macro-shrinkage cavity inside the heat sink, whichforms a thermal barrier and minimize the thermal performance. Using thealuminum alloy of this invention, the internal macro-shrinkage of thedie cast heat sink becomes much less as shown in FIG. 2. Thus, the heatsink fabricated with the aluminum die casting alloy of the invention issuitable for use in CPUs, DRAMs, BGAs, and chipsets. TABLE 4 InputAmbient Case Power Temperature Temperature Rca Material (W) (° C.) (°C.) (° C./W) Mark The alloy 6.625 23.4 90   10.05 Natural of theconvection invention 1070 22.2 94.1 10.85 The alloy 4.2  23.8 70.6 11.14Natural of the convection invention 1070 24.1 74.1 11.9 

[0023] Table 5 shows the fluidity of common die casting aluminum alloysand the alloy of the invention. Table 6 shows the measurement of thermalresistance of a heat sink employing the alloy of the invention and ASTMmaterial A514. It is found that the alloy of the invention has superiorthermal conductivity and fluidity compared to those of common diecasting alloys.

[0024] A514 alloy has a higher thermal conductivity of 138 W/m.K amongthe common die casting aluminum alloys, as shown in Table 2. However,when it is used as a heat sink material, the heat sink has a seriousinternal casting defect including micro-shrinkage and porosity as seenin FIG. 3. In contrast, when the alloy of the invention is employed,there are no casting defects in the heat sink as shown in FIG. 4.

[0025]FIG. 5 and FIG. 6 also show respectively the die cast heat sinksemploying the A514 and the alloy of the invention. It is found thatmisrun occurs when using A514 alloy, but none when using the alloy ofthe invention. Therefore the alloy of the invention has notably superiorthermal conductivity and castability characteristics compared to commondie casting alloys. TABLE 5 Aluminum alloy Fluidity length (mm) A514 250A380 305 A383/A384 320 The alloy of the 350 invention

[0026] TABLE 6 Input Ambient Case Power Temperature Temperature RcaMaterial (Watt) (° C.) (° C.) (° C./W) The 4.95  22.5  90.4 13.72invented Alloy A514 23.2 91  13.70 The 6.625 19.5 102.9 12.59 inventedAlloy A514 23.2 107.7 12.75 The 9.45 23.4 130.1 11.29 invented AlloyA514 23.3 136   11.93

[0027] Moreover, the alloy of the invention contains 0.5-1.2 wt % Fe,which inhibits the metal mold (die) erosion and increases the life cycleof the die. The life cycle between the alloy of the invention and 1070is shown in Table 7. TABLE 7 Material Life cycle of die (metal mold)1070 5,000˜10,000 shots/mold The alloy of the invention Over 50,000shots/mold

[0028] The X-ray diffraction pattern as shown in FIG. 7 it reveals thatthe alloy of the invention exhibited a CuAl₂ phase as compared with theASM Al—Si—Cu reference (eg. A383, A384). The precipitated phase ispossessed of a high thermal conductivity and hardness, which willimprove the thermal behavior and surface flatness when used as a heatsink material. Note that the surface flatness of the heat sink materialalso plays an important role in thermal transfer as it is mounted on thesurface of electric components such as CPU VGA and MCM (Multiple ChipModules).

[0029] While the invention has been described with reference to variousillustrative embodiments, the description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments of the invention, will beapparent to those persons skilled in the art upon reference to thisdescription. It is therefore contemplated that the appended claims willcover any such modifications or embodiments as may fall within the scopeof the invention defined by the following claims and their equivalents.

What is claimed is:
 1. An aluminum die casting alloy comprising 80-90 wt% of aluminum, 9.1-12 wt % of silicon, 4.3-8 wt % of copper, less than0.3 wt % of magnesium, 0.5-1.2 wt % of iron, less than 1.0 wt % of zinc,and less than 0.9 wt % of manganese.
 2. The aluminum die casting alloyas claimed in claim 1 further comprising less than 0.1 wt % of nickel,less than 0.1 wt % of chromium, less than 0.1 wt % of lead, less than0.1 wt % of tin, less than 0.1 wt % of titanium, and less than 0.1 wt %of strontium.
 3. The aluminum die casting alloy useful for a heat sinkcomprising 80-90 wt % of aluminum, 9.1-12 wt % of silicon, 4.3-8 wt % ofcopper, less than 0.3 wt % of magnesium, 0.5-1.2 wt % of iron, less than1.0 wt % of zinc, and less than 0.9 wt % of manganese.
 4. The aluminumdie casting alloy useful for a heat sink as claimed in claim 3 furthercomprising less than 0.1 wt % of nickel, less than 0.1 wt % of chromium,less than 0.1 wt % of lead, less than 0.1 wt % of tin, less than 0.1 wt% of titanium, and less than 0.1 wt % of strontium.
 5. The aluminum diecasting alloy useful for a heat sink as claimed in claim 3 , whereinsaid heat sink is applied to CPUs, DRAMs, BGAs, or chipsets.